Wednesday, December 24, 2008

First things first: Happy Christmas Eve :) Our apologies to our readers who celebrate different festivities this time of year. It's not that we don't want you to enjoy them (although our wishes are probably belated for some), just that we almost forgot about our own... What does that say about us? We don't know either ;) In the spirit of "it's never too late" - Happy Holidays (whatever they may be) from all of us :)

This post is more of an expansion, than a follow-up, to our May 2008 post on using who to find out what and when on Linux and Unix (picking only the options that appeared in most distro's version of "who"). It's also a bit more restrictive than our previous post, as we're restricting the discussion to newer Solaris' (8/9/10) implementation of the classic command (Okay, "according to Hoyle" (and I'm using that idiom loosely, since this post has nothing to do with the game of Whist ;), it can't be a classic for another 12 years, but if TNT can televise "new classics" that just came out last year, the meaning of the word has either been completely devalued or we're making liberal use of artistic license. We prefer the latter justification ;)

Solaris' implementation of who is a great deal better than in older versions, and turns what used to be a "mostly" informational command into a command that you can use to really get to the bottom of things. Following, a list of Solaris who's usage parameters and a brief discussion of each. One thing that should be noted is that the Solaris who command has no "help" switch (-h, --help, nothing), and it will produce output if you just run it without arguments. We usually go with "who -h" (since -h isn't an option) to get usage/help output. You'll have to subject yourself to the humiliating error message, but it's generally worth it ;)

Ladies and gentleman, The Options :)

1.Who straight-up (what better way to start a list of options than with the no-option option? This is what you get if you settle. Four columns: User ID (NAME), terminal (LINE), date (TIME) and local-screen/IP-address:

2. -a. This option is fairly obvious. It stands for "all" and is the equivalent to using "-Abdlprtu" which, the astute among you may have noted, does not comprise the entirety of the options available ;) We'll go over all the options that are lumped together in this option shortly (If I had more time to proofread, I wouldn't have made the word option a tag for this post ;).

3. -b. This option will show you the last time the system booted. This can be very helpful (especially when used in combination with "last -x" to make use of last's full potential):

host # who -b . system boot Dec 8 09:46

4. -d. This option purports to list out "dead" processes. The reason we phrase it in that way is that, generally, these processes (or pseudo terminals) may have been used before, but this doesn't mean that they're hanging around like a bunch of zombie processes. For instance, the following output lists 5 "dead" pseudo terminals, although none of them can be found in the output of either "ps" or "lsof" (???) In any event, it's a cool feature :)

5. -H. This one is a fantastically fun joyride through the land of the obvious. It forces who to print out the header for each column it reports on (although it does forget about the display/IP column noted in straight-up "who" output from point 1):

6. -l. Using who with the -l option lists out only "login" processes. Basically, it will only report on logins that are logged in (or appear to be logged in) to the localhost directly (no external pseudo terminals):

7. -q. This will perform a quick who (only showing the NAME field), and is the only option that the -n option works with. If you use -n with -q, you can specify the number of returned processes you want to see per line of output, at most. By default, who -q tries to return as many results as possible on a single line:

host # who -q user001 user001 user001

who -q -n 2user001 user001user001

8. -r. This option will let you know what run level your system is currently at (again, check out our previous post on using who for more specifics on all of the output "who -r" produces:

host # who -r . run-level 3 Dec 8 09:47 3 0 S

9. -s. This option is considered the "short form," since it doesn't report any "time since last login," session activity status or PID output. who, run with this option alone is actually the default output. The one time this comes in handy is when you're using it with -a (and -H for the headers, if you want), and want to trim that output a bit. Otherwise, using this option wouldn't make sense, since you'd have to specify the flags to print the two fields you want removed ;)

10. -t: This option will show you all the times that your system clock was reset (and, yes, sometimes this output can be empty, for reasons that require no explanation ;)

host # who -thost #

11. -T. This flag shows your tty status (referred to also, above, as session activity status). The + symbol indicates that the tty's status is "writable," the - symbol indicates that the tty's status is "not writable" and the ? symbol indicates general confusion ;) It just means that the system has no idea what the tty's status is, which generally means that it's hung:

12. -u. This flag lists out (and I'm quoting from the "usage" output) "useful information." That isn't to say that any other output you can get from who is completely useless. Although, the terminology does seem to cast a shadow... ;)

13. -m. This flag limits the information to the current terminal session only. As you can see below, we're logged in using pseudo tty /dev/pts/5:

host # who -muser001 pts/5 Dec 23 08:56 (10.99.99.99)

14. And, to begin the wrap-up, Solaris' who makes up for the fact that it doesn't have a built in handler to deal with being called as "whoami" by providing two different options to get that same information. In an alarming show of disregard for proper capitalization, both of these versions work ;) Note that this output is almost always exactly the same as the output from "who -m":

follow that up with the question that, statistically, follows "who am I?" most often, give it a little bit of "Talking Heads" flavour, and you've got yourself a command that's completely useless ;)

host # my God, what have I done?-bash: my: command not found

15. Back off the Road To Nowhere (David Byrne, again. Make him stop!! ;)... Lastly (no pun intended, as you'll understand by the end of this paragraph), you can use who, using any combination of options (with the exception of -n, which only works with -q), and follow it all up with a different utmpx file (if, for instance, your old one got to big and you copied it off somewhere). Straight up who on Solaris makes use of /var/adm/utmpx, but you can tell who to use any utmpx-like file (including wtmpx, which can make the "who" command emulate the "last" command to a basic degree):

Here's hoping today's post help shed a bit more light on Solaris' who options than the standard usage screen does, pointed out a number of reasons it can be a great tool to have in your troubleshooting arsenal and (perhaps) taught you a trick or two :)